Pneumatic control apparatus

ABSTRACT

A pneumatic, proportional, integrating and differentiating control apparatus wherein a rate unit is interposed between the output of an automatic control unit and a negative feed-back circuit and wherein an automatic-manual transfer switch is employed to bypass and cut out the effect of the rate unit at the time of manual operation and to reactivate the rate unit at the time of automatic operation. This control apparatus is constructed so that the transfer switch will operate with a longer time delay than its other automatic-manual transfer switches, which operate substantially instantaneously, when switching from manual to automatic operation and thereby provides bumpless and balanceless manual-automatic switching.

United States Patent 1191 Akiyama et al.

145]. July 16, 1974 PNEUMATIC CONTROL APPARATUS [75] Inventors: Tadashi Akiyama; Ryuhei E'skuda;

Masanobu Ando;1i6rikazu Wada, all of Yokohama; Toshio Umeda, Tokyo; Tatsuhide Shiga, Zushi, all of Japan [73] Assignee: Honeywell Inc., Minneapolis, Minn.

[22] Filed: June 30, 1972 [21] Appl. No.: 268,002

[51] Int. Cl ,1 G05d 16/00, Fl5b 5/00 [58] Field of Search 137/86, DIG. 1,184

[56] References Cited UNITED STATES PATENTS 3,680,580 8/1972 Beardsley 137/86 Primary ExaminerAlan Cohan Attorney, Agent, or Firm-Arthur H. Swanson; Lockwood D. Burton; John Shaw Stevenson [57] ABSTRACT A pneumatic, proportional, integrating and 'diffezesitir ating control apparatus wherein a rate unit is interposed between the output of an automatic control unit I and a negative feed-back circuit and wherein an automatic-manual transfer switch is employed to bypass and cut out the effect of the'rate unit at the time of manual operation and to reactivate the rate unit at the time of automatic operation. This control apparatus is constructed so that the transfer switch will operate 2 Claims, 12 Drawing Figures mil/1.).

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OUT 1) 55 (b) PV:SP DEVIATION PATENTED U 974 SHEEISMS PNEUMATIC CONTROL APPARATUS The present invention generally relates to a pneumatic control apparatus comprising an automatic control unit, a manual control unit and an automaticmanual transferring means, and more particularly to a novel manual to automatic transfer means for the pneumatic control apparatus for effecting a bumpless transfer from manual control to automatic control without a conventional manual balancing operation, that is, a bumpless and balanceless manual to automatic transfer.

The conventional bumpless manual to automatic transfer is realized by means of a manual'balancing operation which adjusts an output of the automatic control unit to such an extent that its value is equal to an output of the manual control unit in manual control mode. j

The present bumpless transferring from'manual-to automatic is made, Without the conventional manual balancing operation, by means of a balancing unit which acts to automatically make the output of the automatic control unit follow the output of the manual control unit in manual control mode. The balancing unit of the bumpless manual to automatic transfer according to the present invention desirably has a high gain characteristic. The present invention uses a pneumatic differential amplifier which is specially designed in order to obtain high gain.

Accordingly, it is the principal object of this invention to provide novel automatic-manual switching means for providing bumpless and balanceless switching from manual control to automatic control, said switching means comprising a special balance unit, transfer switches and-conduits interconnectingthese elements, the automatic control unit and the manual control unit.

Another object of this invention is to provide a new and improved pneumatic proportional integrating and differentiating control apparatus wherein a rate unit is interposed between the output of an automatic control unit and a negative feedback circuit associated therewith, and an automatic-manual transfer switchadapted to short circuit the rate unit at the time of manual operation and to close the rate unit at the time of automatic operation is constructed such that. the transfer switch operates with alonger time than another automaticmanual transfer switches (which operate substantially instantaneouslY) when the operation is switched from manual to automatic operation, thus providing a bumpless and balanceless manual-automatic switching.

In accordance with this invention, there is provided a pneumatic proportional integrating control apparatus comprising an automatic pneumatic control unit with reset means, a manual control unit and automaticmanual transfer means, said automatic-manual transfer means including abalancing unit of the high gain pneumatic differential'amplifier type, a first automatic: manual transfer switch included in an output conduit interconnecting the output of the pneumatic typeautomatic control unit and the output of the control apparatus, a second automatic-manual transfer switch included in a conduit interconnecting the output of the balancing unit and a reset capacitor of the pneumatic type automatic control unit, a conduit interconnecting one input of the balancing unit and the output of the pneumatic type automatic control unit, a conduit for transmitting to the other input of the balancing unit the output from the pneumatic type automatic control unit at the time of automatic control operation, whereas the outputfrom the manual control unit at the time of manual control operation, and a third automatic-manual transfer switch connected in a conduit leading to the output of the manual control unit, whereby, at the time of manual control operation, the output of the pneumatic type automatic control unit is caused to follow up the output of the manual control unit.

According to this invention there is also provided a pneumatic proportional integrating and differentiating control system which is provided by modifying above described pneumatic proportional integrating control system by adding a time delay transfer switch in a conduit connected in parallel with the rate unit of the pneumatic control device. The organization and the operation of the pneumatic control apparatus can be better understood from the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. la shows a pneumatic circuit of one embodiment of the invention;-

FIG. 2 is.a sectional view showing a unique pneu- I matic operational amplifier unit utilized in this invention;

FIG. 3 shows a longitudinal section of a pneumatic switch;

FIG. 4 shows a longitudinal section of a'pneumatic l:l relay;

FIG. 5 is a graph to explain the operation of the pneumatic relay shown in FIG. 4;

FIG. 6 diagrammatically shows a rate unit;

FIG. 7 is a longitudinal sectional view of a balancing unit;

FIG. 8 is a perspective view of an orifice and an oriflee plate utilized in the balancing'unit shown in FIG. 7;

FIG. 9 is a plot showing an input-output characteristic of the balancing unit shown in FIG. 7; and

FIGS. 10a and 10b show the manner of switching the operation mode betweenthe manual mode and the automatic mode.

Referring now to FIG. 1a showing a diagrammatic arrangement of one example of a, PID, proportional integrating and differentiating pneumatic control apparatus embodying theinvention, the control apparatus is illustrated as comprising a pneumatic operational amplifier unit 45 including a nozzle-flapper mechanism having a flapper 68, a pair of air inlet ports 86 and 87, a pair of feedback air inlet ports 88 and 89, and a nozzle 69 for detecting and converting the displacement of a balancing beam 67 into a corresponding output air pressure; a screw throttle R acting as a proportional band adjusting means on the input side; cylindrical fixed throttle R ;transfer switch SW restrictions R and R, which constitute a proportional band adjusting first pneumatic relay 41 and for preventing the leakage of the air pressure from the rate unit to the proportional band adjusting means on the feedback side; a rate off switch 37; a pilot valve 48; a manual control unit 49 for generating desired manualoperating pressure and for following-up the automatic operating pressure at the time of automatic operation; a balancing unit 47 for performing a balanceless and bumplcss manual-automatic switching operation; a delay switch SW for providing the bumpless manual-automatic switching operation for the PID control; automaticmanual transfer switches SW, and SW a manually operated automatic-manual transfer switch SW a manually operated transfer switch SW; which is interlocked with the manually operated automatic-manual transfer switch SW, for transmitting the actuating pressure to the transfer switches SW SW and SW, at the time of automatic operation; and air conduits 1, 2, 3 which interconnects various elements described above. There are also provided a direct-reverse transfer switch D-R for the input pneumatic pressure, a cylindrical fixed restriction R inserted in the conduit 6 which is provided for transmitting the operating air pressure FAS to nozzle 69 and a cylindrical fixed restriction R for delaying the operation of the delay switch SW As shown in FIG. 6, the rate unit 46 comprises a bellows unit 38, a rate throttle R and a rate capacitor C Like the reset throttle R the rate throttle R takes the form of a nozzle-flapper type variable throttle valve. As shown in FIG. la and FIG. lb, the reset throttle R comprisesa nozzle I43, a-flapper I45 fulcrumed by a shoulder of the nozzle, a leaf spring 146 for urging the flapper and means for adjusting the inclination of the flapper which are contained in a casing 144, and an air inlet port 141 and an air outlet port 142. The means for adjusting the inclination of the flapper or the means for adjusting the degree of throttling comprises an eccentric cam 147, which is operated by a knob, not shown, a cam follower 149 and an adjustable screw 148 for connecting one end of the flapper 145 to cam follower 149.

The l:-l pneumatic relay 42 has the same characteristic as relay 4] and has a construction as shown in FIG. 4.More particularly, the interior of a casing 120 is divided into two air chambers 128 and 127 by means of a diaphragm 125 and a nozzle shaped discharge port 126 is provided for chamber 128. An air supply conduit 122 is connected to the air chamber 128 via a restriction 123, whereas the outlet conduit 124 is connected directly to air chamber 128. An air inlet conduit 12] is connected directly to the other air chamber 129.

As shown in FIG. 2, the pneumatic operational amplifier unit 45 comprises a casing 57 which contains a pair of input pressure receiving chambers 51 and 52, a pair of feedback pressure receiving chambers 53 and 54, an input pressure receiving member'75 in the form of a bellows and partitioning chambers 51 and 52, a feedback pressure receiving member or bellows 76 partitioning chambers 53 and 54, and a balancing beam 67 connected to the respective movable ends of the pressure receiving members 75 and 76 so as to displace in response to the received air pressure signals. Two pairs of cylinders 81, 82 and 83, 84 coaxial with the balancing beam 67 are provided in casing 57 along a common axis and these cylinders are vented to the atmosphere. More particularly, cylinders 82 and 83 are constructed integral and vented to the atmosphere through a vent passage 55. These cylinders have the same diameter D. Provision of the vented cylinders requires to hermetically seal all pressure receiving chambers. For this purpose it is advantageous to use rolling diaphragms 71, 72, 73 and 74 with their movable ends connected to balancing beam 67 and the stationary ends to the ends of the cylinders. Pistons 61, 62, 63 and 64 are disposed in respective cylinders. Each piston is connected to the balancing beam 67 such that its head alignes with one end of the corresponding cylinder when the balancing beam assumes a zero position so as to engage the corresponding rolling diaphragm.

The outer diameter of the pistons is important to improve the extent of off-set. As shown exaggerated in FIG. 2 the outer diameter d of piston 64 is smaller than another piston 63 opposing thereto. Another pair of pistons 61 and 62 are constructed to have the same outer diameter d which is equal to that of piston 63. For this reason, it is advantageous to form pistons 62 and 63 as an integral body, as shown in FIG. 2. Accordingly, cylinders 82 and 83 are also made integral.

The purpose of balancing beam 67 is to derive out the resultant displacement of a pair of pressure receiving members 75 and 76.

As shown in FIG. la, throttle R constituting the proportional band adjusting means on the input side is constructed to utilize, as the restricted air passage, a small gap existing between mating male and female screws. The presence of such a small gap is ordinarily inevitable and is not desirable, but in this example, the gap is used to act as a throttle. More particularly, the screw throttle R, comprises a casing 101 provided with fe male screw 102 between an inlet chamber 106 and a discharge chamber 107, a male screw 103 having the same diameter and the screw threads of the same pitch as the female screw 102, and an adjusting member for the male screw having an O-ring. This screw throttle R can be manufactured very easily and can be adjusted readily. FIG. 3 shows a modified switch SW which is constructed to be leak proof. Except for the manual operation, the construction of this switch is substantially the same as that of automatic-manual transfer switches SW SW and SW;,.

The proportional band adjusting circuit on the feedback side is a pressure dividing circuit including a series throttle R and a parallel throttle R,. It is necessary to use throttles having the same characteristic. In this ex ample, both throttles are shown as needle throttle valves, throttle R being fixed whereas throttle R being adjustable. For this reason, the operating knob of the adjustable throttle R, is provided with a suitable scale, not shown. Utilization of a pressure dividing circuit constituted by throttles of the same characteristic greatly improves the linearity of the pressure dividing input output characteristic assumes a line B instead of a line A which corresponds to the one to one ratio. This off-set is caused by the construction of the pneumatic nate the off-set with a single pneumatic relay. More particularly, as shown in FIG. 4, the 1:1 pneumatic relay is provided with an air inlet port 122 and an air discharge port 126 opposing to one side of a diaphragm 125. Whenthe internal diameter and the external diameter of the discharge pipe are denoted by X, and X respectively, the effective area of the diaphragm on the side of the air chamber 128 is decreased by 1r/4 (X,+X /2) For this reason, the 1:1 characteristic curve A will be shifted to curve B as shown in FIG. 5.

The 1:] pneumatic relay 41 should be included in the reset circuit so that its air chamber 129, is connected to reset capacitor C, in order to prevent the air leakage from the reset circuit to the proportional adjusting circuit on the feedback side. If there is some cause that causes the feedback circuit to produce an error of some type, the off-set eliminating function of the improved pneumatic operational amplifier unit 45 would be nullified. For this reason, 1:1 pneumatic relay 42 is included in the negative feedback circuit to oppose the 1:1 pneumatic relay 41 of the same characteristic and included in the reset circuit-acting as the positive feedback circuit thereby producing an off-set free differential output. The l:l pneumatic relay 41 can also be used for the control device including a rate unit for the purpose of preventing the air leakage from the rate circuit to the proportional band adjusting circuit on the feedbackcircuit.

The detail of the constructionof the balancing unit 47 and its orifice portion are shown in FIG. 7 and FIG.

8, respectively, and an input-output characteristic curve of the balancing unit 47 is shown in FIG. 9.

The balancing unit 47 is a pneumatic amplifier of differential operation type which'acts to produce an output pressure signal proportional to' a differential pres- 160 so connected as to be actuated by the beam of the pressure receiving means, a nozzle 161 mounted on a base block 151 so as to face to the flapper 160, spaced therefrom by a distance indicated 'as Xmm, an air passage means 172 for supplying filtered air of a predetermined pressure Ps to the nozzle 161, a restriction 178 of orifice type inserted in the air passage means, and an output conduit 173 for deriving a nozzle back pressure Po from the down stream side of and adjacent to the orifice 178. In this embodiment, the flapper 160 and the beam of the pressure receiving means are constructed integral as shown in FIG. 7. The air passage means includes the conduit 172, air passages 191, 197, 184 and 17.1 and'a chamber 185. The passages 191 and 197 are formed in a plug 175, the passage 184 is formed in aclamping member 176. Passages 171 and 185 are formed in the base block 151. The plug 175 has an ori- 6 fice mounting chamber in which the orifice plate 177 is clamped by the clamping member 176.

The clamping member 176 is provided with the passage 184 of axial bore type and the inner end thereof is provided with several radial ducts 183 for deriving the nozzle back pressure Po. The'clamping member 176 has an engaging portion having a diameter which is the same as the inner diameter of the orifice mounting chamber formed in the one end of the plug 175 so that clamping of the orifice plate 177 is achieved.

"The chamber 185 is formed in the base block 151 by forming a bore therethrough, plugging the plug 175 into one end of the bore and sealing the other end of the bore by means of a metal sealing ball 186. O-rings 196 are provided to surround the plug 175 to interrupt communication between passages 191 and 192 and between passage 191 and the atmosphere. The passage 192 is formed in the plug so as to derive the nozzle back pressure. The output conduit 173 is formed in the base block 151 coaxial with the passage 192. The plug 175 is received in the base block 151 by screw threads 193 and 194. Communication between chamber 185 and passage 192 is interrupted by the engagement between the base block 151 and plug 175 at 196.

The pressure receiving means comprises a pair of pressure receiving chambers 154 and 155, a pair of pressure receiving members 156 and 157 in the form of diaphragms for defining the pressure receiving chambers 154 and 155, respectively, a member 158 engaging these diaphragms for transmitting the displacement thereof to a flapper 160, a supporting member 162 in the form of a leaf spring and a screw 163 for supporting the end of the flapper opposite to the opperating end 163, coil springs 164 and an adjusting screw 165 for imparting a'biasing force of the proper magnitude to the flapper, clamps 159 for the diaphragms'and a pair of air passages 152 and 153 formed inthe base block and The pressure receivingchambers 154 and 155 are constructed identically so as to make equal the effective areas of thediaphragms. Accordingly, the displacement (in the vertical direction as viewed in FIG. 7) of the flapper 160 is proportional to the difference between two input air pressure signals P and P and the direction of the displacement is determined by the sign of the difference ('P,, P In the example shown in FIG. 7', P P the flapper 160 will be displaced up wardly, whereas if P P the flapper will be displaced downwardly. Denoting the displacement of the flapper l in terms ofthe distance X (mm) from nozzle 161 the output air pressure signal P (kg/cm") from the balancing unit 47 of this; .invent ion will vary as shown by a graph of FIG. 9, wherein'the abscissa represents the distance X (mm) between'the nozzle and the flapper and the ordinate represents the output air pressure signal P (kg/cm P shows the pressure of the air supplied to thenozzle which is supplied from a source of clean air at 1.4 (kg/cm' for example. The origin 0 (kg/cm) represents the atmospheric pressure. As can be noted from the characteristic curve shown in FIG. 9, the balancing unit can produce output signals of sub- 7 atmospheric pressure thus increasing the gain as well as the orifice for utilizing the decrease in the air pressure caused by the eddy current of the air produced near the orifice as the output air pressure signal. Further, the construction of the nozzle is advantageous in that it is possible to select any desired value for the distance between nozzle 161 and orifice 178. We have confirmed by experiment that the distance between the nozzle 161 and the orifice 178 does not affect the output characteristic.

In this manner, according to this invention, bumpless and balanceless switching of the operation modes between a, PI, proportional integrating or, PID, proportional integrating and differentiating control unit with an automatic reset, and a manual operator or a manual control unit can be made in the following manner.

. Manual Control The pneumatic circuit of the novel pneumatic control apparatus for the manual control is shown in FIG. lb in which the output OUT from the control apparatus is represented by the output pressure P of manual unit 49. More particularly, for the manual control, since transfer switch SW, is positioned to connect conduit 14 with conduit 15 so that the manual operating pressure P from the manual unit 49 is applied to the pressure receiving chamber of the pilot valve 48 via conduit 14, switch SW conduit 15 and conduit 11 with the result that the pilot valve 48 will provide an output pressure P to the output 40 of the control apparatus via conduit 12. For convenience, it is now assumed that the pilot valve 48 has an input-output ratio of 1:]. Since the transfer switch SW, is positioned to interrupt the communication between conduits 9 and 10, the manual operating pressure P from manual unit 49 is also applied to one of the pressure receiving chambers of the balancing unit 47. Since the transfer switch SW is ON to interconnect conduits l8 and 3 2, the output pressure P from the balancing unit .47-is applied to the reset pressure receiving chamber 54 of the pneumatic operational amplifier unit 45 via conduit 18, transfer switch SW conduit 32, relay 41 and the pressure dividing circuit for the proportional adjustment. As a result, the operational amplifier unit 45 produces an output P,,* for the manual operation which is applied to the other pressure receiving chamber of the balancing unit 47 and to the other feedback pressure receiving chamber 53 of the pneumatic operational amplifier unit 45 via the negative feedback circuit as shown in FIG. 2.

As shown in FIG. 7 the balancing unit 47 has a pair of pressure receiving chambers 154 and 155 so as to produce the output air pressure P by the cooperation of flapper 160 displaced by the pressure differential of two input signals applied to the pressure receiving chambers 154 and 155, and nozzle 161 confronting the flapper 160. The output pressure P varies as shown in FIG. 9 as the gap X" between the nozzle and flapper varies. Since gap X is varied in proportion to the differential pressure between two signals, it is possible to produce output signal P proportional to the difference between said two input signals. Actually, the balancing unit 47 acts as a differential type pneumatic amplifier unit, and the gain and linearity of the input-output characteristic are improved, as shown by FIG. 9, by the unique nozzle shown in FIGS. 7 and 8. As is well known in the art, with the conventional nozzle it is-impossible to produce a subatmospheric output (shown below the abscissa of FIG. 9).

When such a differential amplifier unit of high gains is used as the balancing unit 47, it is possible to cause the output of the operational amplifier unit 45 or the output pressure P,,* of the automatic control unit to follow the output pressure P of the manual unit 49 for manual operation. Let ,u. represent the amplification coefficient of the balancing unit 47 and K5 the propor,

tional gain of the pneumatic control apparatus, following equations hold.

From equations (1) and (2), we obtain (3) Since ,u'and K,, are selected to satisfy conditions ,u. l and K,, ,u., equation 3 can be rewritten as' This means the desired bumpless switching from the manual control to the automatic control. Moreover, it is not necessary to perform any balancing operation which has been necessary in prior art device. Transfer from automatic to manual can be accomplished by rotating interlocked manual transfer switches SW, and SW to the position shown inv FIG. 16. When switch SW is rotated to the position shown in FIG. la, switch operating pressure is supplied from a source of compressed air P to immediately switch ON the first automatic-manual transfer switch SW, and switch OFF the second automatic-manual transfer switch SW However, the third automatic-manual transfer switch SW, is switched from On to OFF with a definite delay time which is determined by the time constant circuit comprising the volume C, of the pressure receiving chamber of switch SW, and the restriction'R in conduit 19 leading to the pressure receiving chamber. This time delay is important to provide the bumpless transfer from manual to automatic of the pneumatic control apparatus with differential action, that is the novel pneumatic PID control apparatus. Generally, since the reset resistance R, is high (in this embodiment, this high resistance is provided by the nozzle-flapper type throttle) immediately after the second automatic-manual switch SW has been switched to OFF by the transfer operation of from manual to automatic, output pressure P from the balancing unit 47 immediately before switching will be stored in the closed circuit comprising conduits 31, 32 and 33, reset capacitor C, and respective chambers in relay 41 and reset throttle R in the reset circuit. Then, if the third automatic-manual transfer switch SW were transferred from manual to automatic concurrently with the transfer of switch SW in the control apparatus via the bellows unit 38 in the reset circuit. However, as abovedescribed, since .the third transfer switch SW closes gradually, in the pneumatic PlD control apparatus too it is possible to provide bumpless transfer from manual to automatic.

AUTOMATIC CONTROL The connection of the novel pneumatic PlD control apparatus at the time of automatic controlis shown by the pneumatic circuit shown in H6. la. When rate off switch 37 is transferred ON, the apparatus operates as a pneumatic Pl control apparatus.

FIGS. a and 10b show the bumpless switching from manual to automatic. In this manner, according to this invention, even in the presence ofa deviation, it is possible to provide bumpless transfer from manual to automatic by a single step operation, that is without the necessity of any balancingoperation.

What we claim:

l. A pneumatic proportional integrating and differentating control apparatus, comprising a pneumatic control unit with automatic reset, a manually operated pressure regulator having an outlet for transmitting fluid pressure of a selected magnitude, an automaticmanual transfer fluid pressure applying means, a balancing unit ofa high gain pneumatic differential amplifier type, said balancing unit having a pair of input ports and an output port, a first fluid pressure operated automatic-manual transfer switch positioned in a first conduit that interconnects each of said input ports of said pneumatic balancing unit, a second fluid pressure transmitting conduit extending between one of said input ports of said balancing unit and an output port of said control unit, a third conduit extending between said output port of said balancing unit and a reset chamber associated with a feedback side of said pneumatic control unit, a second fluid pressure operated automatic-manual transfer switch positioned in said third conduit between the output port of said balancing unit and said reset chamber, a rate unit having an input conduit connected to said second conduit and an output fourth conduit connected to a feedback chamber of said control unit, a third fluid pressure operated automatic-manual transfer switch having a conduit connecting its input side to said second conduit and output conduit connected to said fourth conduit, each of said first, second and third automatic-manual switches being connected by conduits to the output of said automatic-manual transfer fluid pressure applying means, said conduit connecting said pressure applying means to said third switch having a restriction therein to thereby provide a predetermined time delay for actuating said third switch, said conduit connections between the automatic-manual transfer pressure applying means and said first, second and third automaticmanualswitches being effective to immediately close 'said first pressure actuated switch, immediately open said second pressure actuated switch and to effect a time delay in opening said third pressure actuated switch, a fifth conduit connected to another one of said input ports of said balancing'unit and providing an outlet forsaid control apparatus at its other end, a fourth switch associated with said automatic-manual transfer fluid pressure applying means and positioned in a conduit connecting said pressure regulator to said fifth conduit, said fourth switch having passageways therein to transmit an output pressure of a selected magnitude from said manual pressure regulator through said fifth conduit, to one of said inputs of said balancing unit and as an output of said control apparatus during a manual operation of said last mentioned apparatus and to cut off said application of said fluid pressure of said pressure regulator from said balancing unit and said fifth conduit during an automatic operation of said control apparatus.

2. A pneumatic proportional integrating control apparatus as specified in claim 1 and wherein said balancing unit includes a beam, a pressure receiving means for receiving a pair of input pressure signals and which is operative to convert a difference in pressure between s i n yt i nt0 s nespend n d placement of said beam, a nozzle-flapper means connected to a pressure supply means for converting the displacement of said beam into a corresponding output pressure signal which is variable over a range from above atmospheric pressure to below atmospheric pressure, said balancing unit including an orfice plate as a restriction in a passage between the nozzle and the pressure supply means, and

thereby deriving a nozzle back pressure from the down sideqf the o ifice. v v 

1. A pneumatic proportional integrating and differentating control apparatus, comprising a pneumatic control unit with automatic reset, a manually operated pressure regulator having an outlet for transmitting fluid pressure of a selected magnitude, an automatic-manual transfer fluid pressure applying means, a balancing unit of a high gain pneumatic differential amplifier type, said balancing unit having a pair of input ports and an output port, a first fluid pressure operated automatic-manual transfer switch positioned in a first conduit that interconnects each of said input ports of said pneumatic balancing unit, a second fluid pressure transmitting conduit extending between one of said input ports of said balancing unit and an output port of said control unit, a third conduit extending between said output port of said balancing unit and a reset chamber associated with a feedback side of said pneumatic control unit, a second fluid pressure operated Automatic-manual transfer switch positioned in said third conduit between the output port of said balancing unit and said reset chamber, a rate unit having an input conduit connected to said second conduit and an output fourth conduit connected to a feedback chamber of said control unit, a third fluid pressure operated automatic-manual transfer switch having a conduit connecting its input side to said second conduit and output conduit connected to said fourth conduit, each of said first, second and third automatic-manual switches being connected by conduits to the output of said automatic-manual transfer fluid pressure applying means, said conduit connecting said pressure applying means to said third switch having a restriction therein to thereby provide a predetermined time delay for actuating said third switch, said conduit connections between the automaticmanual transfer pressure applying means and said first, second and third automatic-manualswitches being effective to immediately close said first pressure actuated switch, immediately open said second pressure actuated switch and to effect a time delay in opening said third pressure actuated switch, a fifth conduit connected to another one of said input ports of said balancing unit and providing an outlet for said control apparatus at its other end, a fourth switch associated with said automatic-manual transfer fluid pressure applying means and positioned in a conduit connecting said pressure regulator to said fifth conduit, said fourth switch having passageways therein to transmit an output pressure of a selected magnitude from said manual pressure regulator through said fifth conduit, to one of said inputs of said balancing unit and as an output of said control apparatus during a manual operation of said last mentioned apparatus and to cut off said application of said fluid pressure of said pressure regulator from said balancing unit and said fifth conduit during an automatic operation of said control apparatus.
 2. A pneumatic proportional integrating control apparatus as specified in claim 1 and wherein said balancing unit includes a beam, a pressure receiving means for receiving a pair of input pressure signals and is operative to convert a difference in pressure between said input signals into a corresponding displacement of said beam, a nozzle-flapper means connected to a pressure supply means for converting the displacement of said beam into a corresponding output pressure signal which is variable over a range from above atmospheric pressure to below atmospheric pressure, said balancing unit including an orifice plate as a restriction in a passage between the nozzle and the pressure supply means, and thereby deriving a nozzle back pressure from the down side of the orifice. 